The discussion centers on the diffraction pattern produced by a rectangular aperture with varying dimensions (width a and height b). It is noted that the diffraction pattern corresponds to the 2-D Fourier transform of a 2-D step function. The relationship between the dimensions of the aperture (a>b, a<b, a=b) affects the resulting diffraction pattern. Additionally, placing a convex lens at the correct position after the aperture can recreate the image of the aperture, effectively performing an inverse Fourier transform. Understanding these principles is essential for analyzing diffraction patterns in optics.